Capacitive-type line hydrophone



Dec. 20, 1960 J. H. STEIN ETAL 2,965,877

CAPACITIVE-TYPE LINE HYDROPHONE Filed June 10, 1957 INVENTORS JAMES H.STEIN JOHN D. WALLACE ATTORN States CAPACITIVE-TYPE LINE HYDROPHONEJames H. Stein, Auburn, 11]., and John D. Wallace, Oreland, Pa.,assignors to the United States of America as represented by theSecretary of the Navy The invention described herein may be manufacturedand used by or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefor.

This invention relates to line hydrophone apparatus and moreparticularly to an inexpensively constructed line hydrophone for use inthe low frequency range which can be produced conveniently in quantityand made of any desired length.

Low frequency line hydrophones of present design for use when immersedin water or other bodies of conductive liquid generally have verylimited sensitivity as well as one or more construction defects leadingto leakage or undue strain on materials during prolonged pressures.These hydrophones now require special shields to prevent leakagethereinto as well as special materials and fabrication techniques inorder to prevent dielectric rupture.

The present invention overcomes these and other disadvantages of priorconstructions by utilizing an electrode having thereon a woven orlatticed structure forming a large number of dielectric air cells. Thisscreened electrode is then enclosed within an airtight bag of' a pliablematerial for trapping these air cells when under pressure, and also forseparating the water or other liquid outside from the electrode. Thisconstruction provides a large number of small air cells which arecapable of withstanding a considerable pressure before being completelycollapsed. The basic construction is rather simple and inexpensive, andinvolves a minimum of sealing problems.

A first object of the present invention is an inexpensively constructedline hydrophone for use in the low frequency range capable ofwithstanding high pressures over a prolonged period of time.

Another object of this invention is a low frequency line hydrophone forliquid immersion which can be made of any desired length without the useof special materials or fabrication processes.

Still another object of this invention is a line condenser hydrophonefabricated from common and inexpensive materials and capable of useunder the most rigorous conditions.

Other objects and features of this invention will become apparent tothose skilled in the art as the disclosure is made in the followingdetailed description of preferred embodiments of the invention asillustrated in the accompanying sheet of drawing in which:

Fig. 1 shows an isometric view partially cut away of one embodiment ofthis invention.

Fig. 2 shows a fragmentary view along section 22 of the embodiment shownin Fig. 1.

Fig. 3 shows a fragmentary cross section view similar to that in Fig. 2of another form of this invention.

The line hydrophone described herein is generally for use in bodies ofwater to detect and record the presence of sound waves. For example, thedetection of underwater vehicles such as submarines or other vessels by2,965,877 Patented Dec. 20, 1960 their generated noise under conditionswhich make detection otherwise diflicult is made more efiicient by thisdevice. Also, for oil well or other geographical explorations, explosivesounds are made more effective and economical by using the linehydrophone of this invention dipped in an exploratory hole filled withwater or other conductive liquid.

Referring now to the drawing, there is shown in Fig. l the linehydrophone 10 constructed of a fiat, elongated bag or container 12terminating at each end into a pair of solid sections 14 and 16. Thecentral section 18 of hydrophone 10 extends to any desired length asindicated. Within the central section 18 of container 12 is provided alatticed or screened sleeve 20 surrounding a fiat electrode 24.Electrode 24 is made from a conductive material such as aluminum orcopper and may be a foil to facilitate handling and storage, as forexample, aluminum wrap. Container 12 is made from a pliable materialsuch as Pliofilm or polyethylene waterproof bag or lay fiat tubing.Screen 30 is constructed of dielectric material such as a sieve-likeplastic, nylon, or glass material, preferably soft to resist damagingelectrode 24 or bag 12. Screen 20 forms a multiplicity of small aircells 33 against electrode 24 as shown in Fig. 2.

Extending form the opposite side of solid end 14 of container 12 is asolid, extended sleeve 26 which is attached to and may be integral withsection 14. Through sleeve 26 passes an insulated lead 28 which passesthrough section 14 to the interior of hydrophone 10 for connection at 30to the adjacent end 32 of electrode 24. A method for forming the solidend sections 14 and 16 with lead 28 extending through end 14 andproviding sealing which will be satisfactory for the service intendedfor hydrophone 10 is shown in U.S. Patent No. 2,874,- 418 dated February24, 1959, for Method of Fabrication of Condenser Strip Hydrophones, inthe name of Dominic J. Repici. It is understood that a second lead (notillustrated) terminates in the water or othere liquid in whichhydrophone 10 is dipped, as the water or liquid forms the otherelectrode for the device. For this purpose, the exposed end of thesecond lead may be attached anywhere to the outside of hydrophone 10 toinsure the formers immersion along with the latter.

The operation of the device shown in Figs. 1 and 2 is as follows: Withhydrophone 10 immersed in water 34, sound waves or other pressurechanges occurring in the water adjacent to bag 12 cause the latter tomove inwardly or outwardly depending upon the direction of the pressurechange. The capacitance between water 34 and the electrode 24 willchange as a function of the pressure because of the change in size ofthe individual air cells 33. This capacitance change is converted intoan electrical signal by well known techniques. Water 34, which can besweet water having the usual mineral content found in nature, or seawater, is conductive to a sufiicient extent to make hydrophone 10operative when immersed therein.

An alternate construction for line hydrophone 10 which may be suitablefor particular circumstances, is shown in Fig. 3. It consists of asingle sheet of latticed screen 36 similar to screen 20, the electrode24, and the bag 12. A single layer of air cells 33 is formed, andfunctions as in the modification described above.

It will be seen that the constructions described above produce a largenumber of small air cells 33 which are able to withstand considerablepressure before being completely collapsed. In fact, a complete collapseof the air cells 33 would require a physical deformation of electrode 24itself, and with normal construction it has been found that the stressesset up in these parts are resisted up to pressures of a very high order.

Thus, it is seen that there has been provided a novel line hydrophonewhich is capable of use over prolonged periods under high fluidpressures without the necessity of resorting to special or costlymaterials and fabrication processes. The small air cell construction isvery simply and inexpensively formed by the use of screen material,metal foil, and plastic sheet material, all of which are inexpensive andreadily available.

It should be understood, of course, that the foregoing disclosurerelates to only preferred embodiments of the invention and that numerousmodifications or alterations may be made therein without departing fromthe spirit and the scope of the invention as set forth in. the appendedclaims.

What is claimed is:

1. A low frequency, high pressure condenser-type line hydrophonesuitable for being made in any desired length, for being wound on areel, and for being immersed in an electrically conductive fluid mediumwherein the boundary surface of said medium at said transducer acts asone of the electrodes, comprising: only one elongated pliable foil stripof conductive material acting as the other of the electrodes, anelongated pliable watertight envelope of dielectric material flattenedover its entire length in such a manner that its inner surface isadjacent to said foil strip, and an elongated pliable latticed screenwoven of a dielectric material to form a multiplicity of perforations ofsubstantially equal dimensions with respect to each other uniformlydispersed throughout its entire length, said screen beinginterpositioned between at least one flat side of said foil strip andthe inner surface ofsaid envelope in such a manner that the innersurface of said envelope and the one flat side of said foil striptouch.the screen only along its outer sides and thereby forming a multiplicityof confined cells:

of substantially equal dimensions with respect to each other uniformlydispersed throughout its entire length and substantially whereby anysound waves or other pressure changesoccurring in the fluid mediumadjacent to said hydrophone will move said envelope with respect to saidfoil strip to alter the cell dimensions and will produce a change inelectrical capacitance as a function thereof.

2. A low frequency, high pressure condenser-type: line intercellularlynoncommunicating;

hydrophone suitable for being made in any desired length, for being"wound on a reel, and for being immersed in an electrically conductivefluid medium whereby the boundary surface of said medium at saidtransducer acts as one of the electrodes, comprising: only one elongatedpliable foil strip of conductive material acting as the other of theelectrodes, an elongated pliable watertight envelope of dielectricmaterial flattened over its entire length in such a manner that itsinner surface is adjacent to said foil strip, and an elongated pliablelatticed screen woven of a dielectric material to form. a multiplicityof perforations of substantially equal dimensions with respect to eachother uniformly dispersed throughout its entire length, said screenbeing interpositioned between one flat side of said foil strip and theinner surface of said envelope in such a manner that the inner surfaceof said envelope and the one fiat side of said foil strip touch thescreen only along its outer sides and thereby forming a multiplicity ofconfined cells of substantially equal dimensions with respect to eachother uniformly dispersed throughout its entire length and substantiallyintercellularly noncornmunicating; whereby any sound waves or otherpressure changes occurring in the fluid medium adjacent to saidhydrophone will move said envelope with respect to said foil strip toalter the cell dimensions and will produce a change in electricalcapacitance as a function thereof.

References Cited in the file of this patent" UNITED STATES PATENTS1,471,547 Chilowsky et al Oct. 23, 1923 1,584,613 Comstock et a1, May11, 1926 1,966,237 Dinn July 10, 1934 2,571,988 Rupp Oct. 16, 19512,649,579 Alexander Aug. 18, 1953 2,740,032 Bouyoucos Mar. 27, 19562,755,796 Boucke July 24, 1956 2,768,368 Crane et a1. Oct. 23, 1956FOREIGN PATENTS 265,000 Great Britain Feb. 3, 1927 664,775 Great BritainJan. 9, 1952

